kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 110 insertions, 0 deletions

diff --git a/security/tomoyo/load_policy.c b/security/tomoyo/load_policy.c
new file mode 100644
index 000000000..363b65be8
--- /dev/null
+++ b/security/tomoyo/load_policy.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * security/tomoyo/load_policy.c
+ *
+ * Copyright (C) 2005-2011  NTT DATA CORPORATION
+ */
+
+#include "common.h"
+
+#ifndef CONFIG_SECURITY_TOMOYO_OMIT_USERSPACE_LOADER
+
+/*
+ * Path to the policy loader. (default = CONFIG_SECURITY_TOMOYO_POLICY_LOADER)
+ */
+static const char *tomoyo_loader;
+
+/**
+ * tomoyo_loader_setup - Set policy loader.
+ *
+ * @str: Program to use as a policy loader (e.g. /sbin/tomoyo-init ).
+ *
+ * Returns 0.
+ */
+static int __init tomoyo_loader_setup(char *str)
+{
+	tomoyo_loader = str;
+	return 1;
+}
+
+__setup("TOMOYO_loader=", tomoyo_loader_setup);
+
+/**
+ * tomoyo_policy_loader_exists - Check whether /sbin/tomoyo-init exists.
+ *
+ * Returns true if /sbin/tomoyo-init exists, false otherwise.
+ */
+static bool tomoyo_policy_loader_exists(void)
+{
+	struct path path;
+
+	if (!tomoyo_loader)
+		tomoyo_loader = CONFIG_SECURITY_TOMOYO_POLICY_LOADER;
+	if (kern_path(tomoyo_loader, LOOKUP_FOLLOW, &path)) {
+		pr_info("Not activating Mandatory Access Control as %s does not exist.\n",
+			tomoyo_loader);
+		return false;
+	}
+	path_put(&path);
+	return true;
+}
+
+/*
+ * Path to the trigger. (default = CONFIG_SECURITY_TOMOYO_ACTIVATION_TRIGGER)
+ */
+static const char *tomoyo_trigger;
+
+/**
+ * tomoyo_trigger_setup - Set trigger for activation.
+ *
+ * @str: Program to use as an activation trigger (e.g. /sbin/init ).
+ *
+ * Returns 0.
+ */
+static int __init tomoyo_trigger_setup(char *str)
+{
+	tomoyo_trigger = str;
+	return 1;
+}
+
+__setup("TOMOYO_trigger=", tomoyo_trigger_setup);
+
+/**
+ * tomoyo_load_policy - Run external policy loader to load policy.
+ *
+ * @filename: The program about to start.
+ *
+ * This function checks whether @filename is /sbin/init , and if so
+ * invoke /sbin/tomoyo-init and wait for the termination of /sbin/tomoyo-init
+ * and then continues invocation of /sbin/init.
+ * /sbin/tomoyo-init reads policy files in /etc/tomoyo/ directory and
+ * writes to /sys/kernel/security/tomoyo/ interfaces.
+ *
+ * Returns nothing.
+ */
+void tomoyo_load_policy(const char *filename)
+{
+	static bool done;
+	char *argv[2];
+	char *envp[3];
+
+	if (tomoyo_policy_loaded || done)
+		return;
+	if (!tomoyo_trigger)
+		tomoyo_trigger = CONFIG_SECURITY_TOMOYO_ACTIVATION_TRIGGER;
+	if (strcmp(filename, tomoyo_trigger))
+		return;
+	if (!tomoyo_policy_loader_exists())
+		return;
+	done = true;
+	pr_info("Calling %s to load policy. Please wait.\n", tomoyo_loader);
+	argv[0] = (char *) tomoyo_loader;
+	argv[1] = NULL;
+	envp[0] = "HOME=/";
+	envp[1] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
+	envp[2] = NULL;
+	call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
+	tomoyo_check_profile();
+}
+
+#endif